This invention relates to swashplate axial piston hydraulic devices. More specifically, this invention relates to an apparatus and method that provides three operating displacements in a swashplate type axial piston unit.
Present swashplate type axial piston devices comprise a housing having a cylinder block with a plurality of reciprocating pistons therein that are acted upon by a swashplate. The swashplate is connected to a servo piston that is acted upon by a servo spring. Typically, the hydraulic device is a two positioned device in which the swashplate angle is controlled by the servo piston. The maximum angle (displacement) is defined by the point at which the servo piston contacts an end cap of the housing. While the minimum angle is defined by the point at which the servo piston contacts the housing. Thus, the control input is hydraulic pressure and the total movement of the servo piston from minimum to maximum displacement is a predetermined distance. In this embodiment there is no method to control the displacement of the device between maximum or minimum.
With hydraulic technology advancing higher speeds of hydraulic units is being achieved. With greater speeds greater torque loses are experienced as a result of the increase in speed range. Additionally, displacement accuracy of the swashplate has also been diminished as higher speeds have been accomplished causing mistracking problems associated with machines such as crawlers and skidsteer loaders.
Thus, a principal object of the present invention is to provide an improved swashplate type axial piston unit that provides for improved control of the displacement of the device.
Yet another object of the present invention is to provide for multiple functionality of a swashplate type axial piston device.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.